Varenicline tartrate salt, 7,8,9,10-tetrahydro-6,10-methano-6H-pyrazino[2,3-h][3]benzazepine, (2R,3R)-2,3-dihydroxybutanedioate (1:1), has a molecular weight of 361.35 Daltons, and has the following structural formula:

Varenicline tartrate is marketed by Pfizer under the trade name of CHANTIX™ as a partial agonist selective for certain subtypes of nicotinic receptors and indicated for smoking cessation.
Varenicline base, 5,8,14-Triazatetracyclo [10.3.1.02,11.04,9]hexadeca-2(11),3,5,7,9-pentaene and a variety of salts thereof are disclosed in U.S. Pat. No. 6,410,550, EP 1044189, and EP 1659114.
Varenicline citrate and succinate salts are described in U.S. Pat. Nos. 6,787,549 and 6,794,388, respectively. A Crystalline form of Varenicline fumarate is described in PCT Publication No. WO2009/109651.
Varenicline L-tartrate and its crystalline forms A, B, and C are described in the U.S. Pat. Nos. 6,890,927 and 7,265,119.